1. Field of the Invention
The present invention relates to a method of inspecting a porous structure.
2. Description of the Related Art
A ceramic honeycomb structure has been widely used as a dust collecting filter for use in applications such as a pollution preventing environment countermeasure and product recovery from a high-temperature gas in various fields including chemical plants, electric power plants, iron and steel works, and disposal for industrial waste since it has a superior heat resistance and corrosion resistance. For example, a diesel particulate filter (DPF) for capturing particulates discharged from a diesel engine and the like are used under severe conditions such as high temperature and corrosive gas atmosphere, and therefore a ceramic honeycomb structure has been preferably used.
Especially in recent years, from a necessity of enhancing process capability of a dust collecting filter, there has been a demand for a ceramic honeycomb structure having a low pressure loss and a high porosity, and having required levels of an average pore diameter and pore volume in accordance with a dust collection performance as well. As a method of manufacturing a ceramic honeycomb structure (porous honeycomb structure) having a high porosity, a method of manufacturing a porous honeycomb filter has been proposed in which a mixture of a binder (organic binder such as methyl cellulose), a pore forming agent (organic material such as graphite) and the like, in addition to aggregate particle materials such as cordierite forming material and water, are kneaded to form a plastic material having plasticity, and the resultant is dried, and fired (see JP-A-2002-219319).
Moreover, a ceramic filter has been used in order to remove bacteria and particulates of waste contained in sewage for purification. For example, a ceramic porous article is preferably used in a final step for purifying drinking water in a water purification plant. Thus, there has been a demand for a ceramic filter having a high porosity, and the required levels of an average pore diameter and pore volume in accordance with filtering capability in order to enhance a filtering amount even in the purification of the drinking water.
Usually, the pore characteristics of a formed article obtained by extrusion are inspected to assure that a porous structure as a product can satisfy the predetermined levels of the characteristics as to pore (the characteristics as to pore is hereinafter referred to as pore characteristics) inclusive of the porosity, the average pore diameter, the total pore volume and the like of the porous structures produced. In the inspection, sampling inspection has been mainly performed by using measurement methods such as an Archimedes process and mercury press-in porosimeter.
However, in the case of the produced structures obtained by the extrusion, in the sampling inspection, there remains a possibility that the products having defects in the pore characteristics are sent to the users or the next step. For example, in a case where sudden troubles such as changes in subtle forming conditions occur during the extrusion, such as for example, unusual operation state of a kneader, there has been a problem that the products having defects are sent at a relatively high probability to the users or the next step.
Moreover, since the measurement methods using Archimedes process and the mercury press-in porosimeter require not only special devices and techniques but also the laborious procedures and costs, it has been actually difficult to carry out a total inspection.
Furthermore, after the sampling inspection, both end faces of the formed article should be alternately plugged in a checkered pattern flag-like manner. Thus, the plugging is performed in vein as far as the porous structures having defects overlooked due to the sampling inspection are concerned. This has caused cost increases.